1. Field of the Invention
The present invention relates to an image expanding apparatus and a method thereof for restoring a compressed code of an image to an original image, in particular, to those according to the JPEG (Joint Photographic Experts Group) 2000 system.
2. Description of the Related Art
The JPEG system, which is a conventional image encoding system, uses DCT (Discrete Cosine Transform) and Huffman codes of zero run lengths and values of DCT coefficients as engineering elements. Due to characteristics of the encoding system, the codes cannot be directly changed. Thus, when some change is desired to be made for an image, it is necessary to expand the image, change the expanded image, and then re-encode the changed image. In contrast, the JPEG 2000 system, which is a new encoding system, uses a wavelet transform and a tile architecture that allow an image size and an image range to be easily changed.
The specification of the JPEG 2000 system is described in “JPEG 2000 Image Coding System”, Information Technology, ISO/IEC JTC 1/SC29/WG 1, JPEG 2000 Part I Final Committee Draft Version 1.0, Mar. 16, 2000 (reference 1).
In the JPEG 2000 system, an image is divided into at least one tile. Each tile is transformed according to the discrete wavelet transform (DWT). Wavelet transform coefficients are arithmetically encoded for each bit map. In addition, the wavelet transform is performed for image at multiple stages. As shown in FIG. 1, an image is divided into an LL1 component, an LH1 component, an HL1 component, and an HH1 component. The LL1 component is sub-divided into an LL2 component, an LH2 component, an HL2 component, and an HH2 component. Each component is further sub-divided a plurality of times. In the example shown in FIG. 1, the LH1 component, the HL1 component, and the HH1 component compose a resolution level R3. The LH2 component, the HL2 component, and the HH2 component compose a resolution level R2. The resolution, the image size, and the number of gradation levels of the code of the JPEG 2000 system are scalable.
A code stream of the JPEG 2000 system is composed of one main header and a plurality of tile streams. Each tile stream is composed of one tile header and one packet stream. Each packet stream is composed of a plurality of packets. Each tile stream may be composed of a plurality of tile parts. In this case, the beginning tile part is composed of one tile header and a plurality of packets. Each of the second and later tile parts is composed of one tile part header and a plurality of packets.
The main header is composed of SOC (start of code-stream), SIZ (image and tile size), COD (coding style default), QCD (quantization default), COC (coding style component), QCC (quantization component), RGN (region of interest), POC (progression order change), PPM (Packed packet header: main header), PLM (packet length: main header), TLM (tile-part lengths: main header), CRG (component registration), and COM (comment). However, only SOC, SIZ, COD, and QCD are mandatory. The others are optional. The tile header is composed of SOT (start of tile), COD (start of code), QCD (quantization default), COC (coding style component), QCC (quantization component), RGN (region of interest), POC (progression order change), PPT (packed packet headers: tile-part), PLT (packet length: tile-part), COM (comment), and SOD (start of data). However, only SOT and SOD are mandatory. The others are optional. The tile part header is composed of SOT (start of tile), POC (progression order change), PPT (packed packet headers: tile-part), PLT (packet length), COM (comment), and SOD (start of data). However, only SOT and OSD are mandatory. The others are optional.
The compound image file format of the JPEG 2000 system is described in “JPEG 2000 Image Coding System: Compound Image File Format”, Information Technology, JPEG 2000 Part 6 FCD, ISO/IEC JTC 1/SC 29/WG1, Nov. 16, 2001 (reference 2). With a compound document file, individual portions of a page that contains text and an image can be compressed in different compressing systems.
According to the reference 2, a compound document file (JPM (JPEG 2000 File Format-Multi-layer) file) has a structure as shown in FIG. 2. One Page box (B.2.1) can contain any number of Layout Object boxes (B.3.1). One Layout Object box (B.3.1) may contain at least one Object box (B.4.1).
Japanese Patent Laid-Open Publication Nos. 2002-152517 (reference 3) and 2002-152744 (reference 4) disclose “Image expanding apparatus for transformed code” and “Image expanding method for transformed code”.
However, according to the inventions disclosed as the foregoing references 3 and 4, a generated parameter of an original image cannot be obtained. Thus, an image cannot be optimally expanded. In addition, these inventions do not deal with a multiple layout object structure of an image. A layout object is defined as Object box (B.4.1) in the reference 2.